To date, there are combined air-conditioning and hot-water supply systems that can simultaneously provide a cooling load, a heating load, and a hot-water supply load by using a single stage refrigeration cycle. As such a system, there is proposed “a multifunctional heat pump system including a refrigeration cycle that enables a cooling or heating operation, a hot water supply operation, a heat storage operation, and a cooling storage operation to be performed separately and simultaneously by using a refrigerant circuit that includes a compressor and in which the compressor, an outdoor heat exchanger, an indoor heat exchanger, a cooling energy storage tank, and a hot-water supply heat exchanger are connected to one another” (see Patent Literature 1, for example).
Among such systems, a system having the following configuration has been proposed (see Patent Literature 2, for example). In the system, a bypass pipe including a bypass solenoid valve installed in parallel with a hot-water supply heat exchanger is disposed between inlet and outlet ports of a refrigerant pipe connected to the hot-water supply heat exchanger. An amount of influx of refrigerant for hot-water supply into the hot-water supply heat exchanger is controlled by opening and closing the bypass solenoid valve for influx of the refrigerant for hot-water supply into the bypass pipe. If the surface temperature of the outdoor heat exchanger is equal to or lower than a temperature preset for performing a defrosting operation, the bypass solenoid valve is opened to allow the refrigerant for hot-water supply to flow into the bypass pipe.